1. Field of the Invention
This invention relates to the field of nonvolatile analog magnetic memories. Specifically this invention avoids the use of moving mechanical parts or moving magnetic domains or bubbles or any form of digital storage.
2. Description of the Prior Art
Man's first methods of analog data storage included counting on fingers as well as simple written representations of numbers counted. The most common current form of analog data storage is magnetic tape, where information embodied as electromagnetic signals is magnetically written onto the tape, and magnetically read when the data is later needed. The current process of writing and reading analog data on tape is slow in comparison to the current computer, microelectronic, semiconductor technology. In addition the tape nonvolatile analog format must be electromechanically written and read which allows opportunity for unreliability. The linear action of tape precludes the possibility of random accessibility. Methods of converting analog information into digital formatted data for storage of the original analog data in digital memories has been developed using analog to digital converters. Digital dynamic, digital static, and digital nonvolatile memories are used for the actual storage of analog data which has been converted to digital format. When data is retrieved from it's digital format, it is converted back to it's original analog format by a digital to analog converter. Digital random access cell arrays on substrates exist to store large amounts of information, but in all cases there are only two types of data storable in any one cell, an on signal or an off signal. This requires the inefficient use of many cells to store a piece of analog data since it is impossible to represent a unique piece of analog data as a simple on or off signal. There is no way to differentiate differing pieces of analog data. Bubble memories and all dynamic, static, and nonvolatile random access memories currently in art are all digital in nature with limited storage per cell of an on state or an off state only.
In addition to the foregoing memory systems the "Sheet Random Access Memory", U.S. Pat. No. 4,791,604 discloses a nonvolatile memory system comprising a substrate including a plurality of ferromagnetic domains and a corresponding plurality of distinguishable locations, and a fixed drive device to selectively generate an electromagnetic field within the substrate of a selected one of the distinguishable locations in order to alter the ferromagnetic domain into one of at least two distinct magnetic configurations corresponding to a 0 and a 1. This is clearly a digital device despite the use of magnetic domains and the possible use of a Hall effect device as part of the fixed sensing portion of this device.
In another example shown by Shu-Yau ET AL, "Ferroelectric Memory Device" U.S. Pat. No. 3,832,700, the abstract reads; A ferromagnetic memory device utilizing the remanent polarization of a thin ferroelectric film to control the surface conductivity of a bulk semiconductor and perform the memory function. The structure of the device is similar to a conventional MIS field effect transistor with the exception that the gate insulating layer is replaced by a thin film of active ferroelectric material comprising a reversibly polarizable dielectric exhibiting Hysteresis. This too is clearly a digital memory.
In another example shown by Prinz, "Thin Film Magnetic Memory Elements" U.S. Pat. No. 5,025,416, the summary of the invention states; The memory element also includes a means for magnetizing the closure domain in one of a first and second directions, whereby said closure domain can be magnetized in the first direction, indicating a "1" bit or the second direction, opposite the first direction, indicating a "0" bit. Another clearly digital memory.
In another example Heywang states in "Field Effect Transistor with a Ferroelectric Control Gate Layer" U.S. Pat. No. 3,426,255. The semiconductor device illustrated in FIG. 1 can therefore be switched from high conductivity of forward conductance to low conductivity or the blocked state and vice versa, each time by applying an electrostatic field whose direction is reversed relative to one previously effective and whose strength suffices to overcome the remanent polarization. Again a digital device.
In a final example Arndt in "Nondestructive Memory With Hall Effect Readout" U.S. Pat. No. 3,521,255 states; by a "permanently magnetizable material" I mean a material which may by the impression of magnetizing flux thereon, acquire a polarity of magnetization which it will retain until magnetizing flux of more than a predetermined amount, of the opposite to the original polarity is applied, at which time the polarity of magnetization may be switched, and where the switching may be repeated in the same manner . . . "thus the state of the field may indicate one or the other of the binary states and may be read out in the manner set out above. Another clearly digital device.
What is needed is a simple analog nonvolatile magnetic memory which is truly transportable which does not require the use of electromechanical parts for writing and reading, which is very easily compatible with existing electronic circuit technology and computer systems.